I already wrote. The temperature is normal but the problem remains. I had a copy of an almost clean system and ran it all night yesterday. The system did not hang but vnc stopped working after 6 hours. Interestingly, the session is active, the log says nothing about errors and you can't connect. Restarting systemctl tightvncserver also doesn't help, is it a port sharing problem? P.S. Before installing the fan, the temperature was up to 72C!